Insight into antibiotic degradation through photocatalysis processes: Photocatalysts semiconductors, transformation products and influencing factors

Abstract

Abstract Population growth and globalization have led to increasing demands for antibiotics to treat bacterial infections. However, the excessive use of these drugs and their continuous discharge into the aquatic environment now comprise a significant concern, in view of the development of resistant microorganisms. In this scenario, photocatalytic processes comprise an interesting alternative for removing antibiotics from the aquatic environment, due to their high efficiency and non-toxicity. This review discusses recent heterogeneous photocatalysis trends and applications aiming at the removal of the main antibiotics commonly found in aquatic environments (Sulfamethaxazole - SMX, Ciprofloxacin - CIP and Tetracycline - TET). Studies assessing optimal operating conditions, the different photocatalysts (TiO2, ZnO, VO4, WO) used during the process, pH values, matrix effects, transformation products and residual antimicrobial activity are examined. Reaction mechanisms are detailed for each antibiotic, although only 12% of the articles included in this review assessed potential reaction mechanisms. Even though high antibiotic removal efficiencies are reported, residual antibacterial activities are still persistent following photocatalytic processes. Furthermore, studies lack a broader approach in evaluating photocatalytic antibiotic degradation efficiencies. In addition to evaluating parent molecule degradation and reaction parameters, further assessments employing more complex matrices (conducted in only 5% of the included studies) and environmentally relevant contaminant concentrations are also required. The main contribution of this review consists in explaining the relationship between antibiotics and photocatalysis applications and in outlining ways to remove antibiotics from wastewater for safe reuse, meeting United Nations Sustainable Development Goals (SDG 6).